1. Field of the Invention
The invention relates to a process for the preparation of antimony of high purity in which the antimony (III) oxide is dissolved in an aqueous alkaline solution and the solution is subjected to electrolysis.
2. Description of the Prior Art
Antimony of high purity is required for antimony alloys, for use as semiconductors. A process for the preparation of antimony of high purity of the type mentioned at the beginning is disclosed in German Offenlegungsschrift No. 2,063,307. This process starts with antimony(III) oxide which is obtained by burning refined metal and which is treated with dilute nitric acid with stirring, before it is dissolved in an aqueous, alkaline solution of glycerine and sodium hydroxide. After allowing the mixture to settle, the solution is drawn off and the undissolved antimony(III) oxide is washed with water. The solution with the dissolved antimony(III) oxide is electrolyzed using pure graphite as the anode and antimony of a high degree of purity as the cathode.
The efficiency of this process is relatively poor since the electrolysis can only be carried out till the electrolyte content decreases to 60 to 80 g Sb/l electrolyte. Then, the electrolyte must be concentrated again to 100 g Sb/l. A further significant disadvantage of this process is due to the dissolution of the graphite anodes after a short period of electrolysis. As a consequence, finely divided carbon is produced and is essentially distributed throughout the electrolyte. In order to prevent a deposition of this carbon together with the antimony, an additional filtration of the electrolyte is necessary which step is quite costly. Moreover, high costs also result from the high consumption of the graphite anodes.